1. Field of the Invention
This invention relates to polymer/polyol compositions and to polyurethanes utilizing such polymer/polyol compositions.
2. Description of the Prior Art
Polymer/polyol compositions suitable for use in producing polyurethane foams, elastomers and the like are known materials. The basic patents in the field are Stamberger Re. 28,715 (reissue of U.S. Pat. No. 3,383,351) and Re. 29,118 (reissue of U.S. Pat. No. 3,304,273). Such compositions can be produced by polymerizing one or more ethylenically unsaturated monomers dissolved or dispersed in a polyol in the presence of a free radical catalyst to form a stable dispersion of polymer particles in the polyol. These polymer/polyol compositions have the valuable property of imparting to, for example, polyurethane foams and elastomers produced therefrom, higher load-bearing properties than are provided by the corresponding unmodified polyols.
The polymer/polyol compositions that found initial commercial acceptance were primarily compositions produced using acrylonitrile. Many of these compositions were somewhat higher in viscosity than desired in some applications. More recently, polymer/polyol compositions produced from acrylonitrile-styrene monomer mixtures have been used commercially.
Polyurethane foams made with polymer/polyols are widely utilized. The two major types of foam are generally termed slabstock and molded. More particularly, slabstock foams employing polymer/polyol compositions are used in the carpet, furniture and bedding industries. One primary use of slabstock foam is as carpet underlay.
In the molded foam area, the primary type of foam employed is generally termed high resiliency (HR) molded foam. HR molded foams have been widely used in the automotive industry for applications ranging from molded seats to energy-absorbing padding and the like.
The wide demand for polymer/polyols has spawned a number of trends that have created the need for additional technology. For example, the general trend is to provide slabstock foams that are virtually scorch-free, i.e.--white foam products. Indeed, the desire is to provide techniques capable of producing, without substantial economic penalty, virtually scorch-free foams at ever-decreasing densities (viz.--1.5 pounds per cubic foot or less) while maintaining satisfactory load-bearing and other foam properties.
Such scorch-free foams have been obtained by utilizing relatively high styrene contents (e.g.-- about 65 to 70 percent styrene) in the acrylonitrile-styrene monomer mixture. The utilization of such high styrene monomer mixtures in the molded foam area is also widespread.
The preparation of polymer/polyols from such high styrene monomer mixtures creates difficulties. More particularly, such difficulties arise due to the state of the art to which polyurethane production has now advanced. There is now concern over the degree of the stability of polymer/polyol compositions. Many applications require somewhat rigorous stability characteristics, and such characteristics become more difficult to achieve when high styrene monomer mixtures are employed.
A further trend is the desire to provide foams with ever-increasing load-bearing characteristics for many applications. This is particularly prevalent in the slabstock area where many formulations require the use of "neat" polymer/polyols, i.e.--the polymer/polyol is employed without dilution with conventional polyols. While typically not used neat in the molded foam area, polymer/polyols capable of imparting higher and higher load-bearing characteristics to such foams are likewise desired.
Such increased load-bearing characteristics are being obtained by increasing the polymer or solids content of the polymer/polyol. Solids contents of 35 to 40 weight percent or even more are accordingly desired. Preparing such high solids content polymer/polyols with the degree of stability often desired becomes substantially more difficult as the solids content is increased.
The trend toward the use of high styrene monomer mixtures and high solids content polymer/polyols has likewise resulted in polymer/polyols sometimes having higher than desired viscosities. The viscosity of a polymer/polyol must, of course, be sufficiently low to allow ease in handling during manufacture. Moreover, the viscosity must allow ready transport, handling and, ultimately, adequate processability in the foam processing equipment being utilized. The viscosity level is becoming of acute concern in the molded area due to the sophisticated mixing systems, such as impingement systems, that are increasingly being utilized. There is a clear need to provide the desired polymer/polyols with as low a viscosity as possible.
Also, the degree of stability of the polymer/polyol, as alluded to previously, is of concern. At one time, there was not much concern for the seediness or filterability of polymer/polyols in actual commercial practice. However, the state of the art of polyurethane production has now advanced to the point where these considerations are very important in many applications. This is particularly important in the molded foam area.
Thus, the development of sophisticated, high-speed and large-volume equipment, machines and systems for handling, mixing and reacting polyurethane-forming ingredients has created the need for highly stable and low viscosity polymer/polyols. Polymer/polyols must accordingly meet certain minimum requirements in order to be capable of being satisfactorily processed in the sophisticated foam equipment now used. Typically, the prime requirement is that the polymer/polyols possess sufficiently small particles so that filters, pumps and the like do not become plugged or fouled in relatively short periods of time.
While somewhat simplified, the commercial processability of a particular polymer/polyol comes down to its stability against phase separation, i.e., the polymer particles settling out of the polyol medium. Stability of the dispersion is thus a prime consideration in insuring that the polymer/polyols can be processed in commercial production equipment without the necessity of additional mixing to insure uniformity.
Since the basic development by Stamberger, a substantial amount of effort has been devoted to providing improved polymer/polyols and to improved preparation techniques. For example, U.S. Pat. No. 4,208,314 to Priest et al. discloses low viscosity polymer/polyols made from acrylonitrile-styrene monomer mixtures. These polymer/polyols can be converted to low-density, water-blown polyurethane foams having reduced scorch, especially when the acrylonitrile-to-styrene ratio is relatively low. The Priest et al. patent also provides a process for making polymer/polyols whereby the particulate nature of the polymer portion of the product is considerably improved, compared to polymer/polyols prepared by prior processes. The improved process provided by Priest et al. includes, in general, maintaining a low monomer to polyol concentration throughout the reaction mixture during the polymerization.
A further improvement in the formation of polymer/polyols is provided by U.S. Pat. No. 4,148,840 to Shah. This discloses a process for producing highly stable and filterable polymer/polyol compositions by polymerizing the monomer or monomers in situ in a polyol mixture that includes a minor amount of preformed polymer/polyol.
It has been recognized that the stability of polymer/polyols requires the presence of a minor amount of a graft or addition copolymer which is formed in situ from growing polymer chains and polyol molecules. Some prior approaches have thus been directed to incorporation of unsaturation into the polyol in addition to that inherently present in the polyoxyalkylene polyols typically used in forming polymer/polyols in the belief that improved stability will result due to an increased amount of an addition copolymer stabilizer expected to be formed. U.S. Pat. Nos. 3,652,639, 3,823,201, and 3,850,861, British Pat. No. 1,126,025 and Japanese Pat. Nos. 52-80919 and 48-101494 all utilize this approach.
In a similar vein, the use of what may be termed "stabilizer precursors" has been proposed. More specifically, the concept is to carry out the preparation of the polymer/polyol in the presence of a suitable amount of the stabilizer precursor, which precursor comprises what has been termed a "macromer" that contains a particular level of reactive unsaturation. The belief is that, during polymerization in the preparation of the polymer/polyol, adequate amounts of stabilizer will be formed by the addition polymerization of the precursor stabilizer with a growing polymer chain. The concept of using stabilizer precursors in polymerization is a well-recognized and old technique as discussed in "Dispersion Polymerization in Organic Media", edited by K. E. J. Barrett, John Wiley & Sons, copyright 1975. U.S. Pat. Nos. 4,454,255 and 4,458,038 are recent examples utilizing this technique. The macromer in the '255 and '038 patents may be obtained by reacting a polyol with a compound having reactive ethylenic unsaturation such as, for example, maleic anhydride or fumaric acid. A further example of the use of this technique is U.S. Pat. No. 4,460,715. The reactive unsaturation in the '715 stabilizers is provided by an acrylate or methacrylate moiety.
The use of chain transfer agents in the preparation of polymer/polyol compositions has been proposed for a variety of purposes, including reaction moderation and lowering the viscosity of such compositions. Various chain transfer agents, including mercaptans, alcohols, and the like have been suggested.
For example, U.S. Pat. No. 3,655,553 discloses a polymer/polyol prepared by the grafting of a mixture of vinyl chloride and vinylidene chloride onto a polyol such that the resulting polymer/polyol dispersion has a chloride content of at least 15% by weight. From 0 to 5 weight percent of a chain transfer agent may be used. It is stated that the viscosity of the grafted product can be reduced by the presence of a chain transfer agent during the polymerization. A number of chain transfer agents are described as being suitable, including halogenated hydrocarbons, mercaptans, aldehydes, and the like.
U.S. Pat. No. 3,850,861 discloses a polymer/polyol prepared from an unsaturated polyether polyol in which the polymerization can be carried out in the presence of a chain transfer agent in an amount sufficient to prevent the formation of higher-than-desired molecular weights.
U.S. Pat. No. 3,953,393 discloses a polymer/polyol prepared by the in situ polymerization of a vinyl monomer in an unsaturation-containing polyol in the presence of an alkyl mercaptan chain transferring agent. The dispersions are stated to have lower viscosity than those of the prior art.
In U.S. Pat. No. 4,144,840, it is stated that the polymer/polyols disclosed therein can be prepared in the presence of any known chain transfer agent, if desired. The polymer/polyol compositions have low viscosities with relatively high polymer contents.
U.S. Pat. No. 4,230,823 discloses the use of certain enol ethers as chain transferring agents in the preparation of polymer/polyols to provide a relatively low viscosity polymer/polyol even at a relatively high solids content. It is noted that the alkyl mercaptans commonly suggested for use in preparing polymer/polyol compositions do not provide the desired lower viscosity of the polymer/polyol because the mercaptans compete with the polyether polyol as transferrers with a high transfer content.
Further, U.S. Pat. Nos. 4,454,255 and 4,458,038 are directed to low viscosity, white graft polymer dispersions having a high polymer content made by polymerizing an ethylenically unsaturated monomer or mixture of monomers in a polyol mixture which includes a polyoxyalkylene polyether polyol and a macromer containing induced unsaturation. It is stated that chain transfer agents may be employed as "reaction moderators," suitable chain transfer agents including, among others, isopropanol, ethanol, 1-butanol, carbon tetrachloride, and the like.
Still further, U.S. Pat. No. 4,014,846 describes the synthesis of finely divided polymeric solids in various solvents, including isopropanol and methanol. The solids are then dispersed in polyol to form the dispersion.
A further concern that polyurethane producers must address is the combustibility resistance standards that must be satisfied for many applications. In the slabstock foam area, perhaps the most commonly employed standard is the well known California Vertical Burn test. To attempt to satisfy this rigorous standard, polyurethanes prepared using polymer/polyols have historically required relatively high levels of flame retardants. Such flame retardant levels represent an obvious economic penalty, and such levels can be so excessive as to adversely affect other desired foam properties. Moreover, even with the use of relatively high flame retardant levels, satisfying the California test criteria can be problemmatical.
In the molded foam area, the typical standard utilized is the Federal Motor Vehicle Safety Standard (FMVSS) No. 302. Attempts to satisfy this standard have, in the past, utilized relatively moderate levels of flame retardants. However, more recently, due to instability of suitable flame retardants in polyurethane premixes resulting in the requirement for separate metering, the need was created to provide polymer/polyols capable of satisfying this test without using any flame retardant additive.
Simroth et al., U.S. Pat. No. 4,463,107, discovered that improved combustion resistance of polyurethane foams could be obtained if the structural properties of the polymer portion of the polymer/polyol is adjusted to provide a crosslinking coefficient below about 55. The reduction of the crosslinking coefficient to the desired level may be accomplished by controlling a variety of process parameters, including the free radical polymerization catalyst concentration, the residence time, the ratio of acrylonitrile-to-styrene, and/or by the utilization of a variety of chain transfer agents. Utilizing the '107 invention provides polymer/polyols which, upon conversion to polyurethanes, can readily satisfy the FMVSS-302 standard without using flame retardant additives. Moreover, polyurethanes made from polymer/polyols using the '107 invention can readily pass the California test with moderate and acceptable flame retardant levels. Indeed, utilizing this invention may even allow the California test to be satisfied without the addition of flame retardants.
Unfortunately, it has been found that use of these techniques can impact upon the tensile properties of the foam, i.e.--the tensile and tear strengths and elongation. Indeed, this impact can be enough to reduce the tensile properties to levels below those considered desirable for certain applications.
Moreover, in addition to the combustibility resistance concern, the trends discussed herein have created the need for additional technology to allow preparation of the desired polymer/polyols in a commercially attractive fashion.